Idiot proof - no ports that can be compromised...
No USB, Thunderbolt or Firewire, no optical drive, and you need an adapter cable to even connect to the thing.
So no danger of rootkits and the like via those ports/discs, no nuisances like malware, adware or compromised versions of XCode or other disturbing stuff coming from USB sticks...it helps keep the machine a bit clean, and that is also very useful in a managed environment. Streaming or downloading any kind of content works fine over WiFi. The OS is installed, upgraded and even recovered from Apple's site using the internal recovery disk partition, so no need for install media there either.
With the high res screen, light weight and long battery life, it seems ideal for all those people who just need a laptop to do basic office type stuff on the go.